JPH11310845A - High Young's modulus low expansion cast iron and method for producing the same - Google Patents

Abstract

(57) [Problem] To provide a high Young's modulus low expansion cast iron having improved Young's modulus while maintaining low expansion properties, and a method for producing the same. SOLUTION: In weight%, C: 0.6 to 2.0%, Ni:
25-40%, Co: 0.1-12.0%, Ni + C
o: 34 to 40%, Si: 1.0% or less, Mn: 1.0
% Or less and Ti, Zr, Hf, V, Nb, Ta, C
One or several kinds of metal elements selected from r, Mo and W are used alone or in combination to contain 0.5 to 6.0%, the balance being Fe and unavoidable impurities, and having a solid solution carbon content of 0%. .4% or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high Young's modulus low expansion cast iron having a low coefficient of thermal expansion near room temperature and an improved Young's modulus, and a method for producing the same.

[0002]

2. Description of the Related Art Cast iron is widely used as a basic material in the industry. Cast iron is excellent in castability, can be formed in various complicated shapes, and is easy to cut.
This is because there are advantages that the cost required for processing and dissolving the material is relatively inexpensive, and that it can be easily manufactured even in a small-scale factory.

[0003] In recent years, with the development of the electronics industry, machine tools, precision measuring instruments, molding dies, scientific instruments, and other manufacturing machines related thereto are required to have materials with higher precision and excellent functions. It became so.

In particular, there is an increasing demand for improving the dimensional accuracy of components such as semiconductor manufacturing equipment, and it is important to take measures against material deformation against thermal deformation. As a countermeasure, low-expansion cast iron having a low coefficient of thermal expansion in a temperature range from room temperature to 300 ° C. is being widely used. As a typical material with excellent low expansion properties,
An invar alloy (35% Ni-Fe alloy) has been developed, and a super-invar alloy (31% Ni-5% Co-F) in which a part of Ni has been replaced with Co to improve low expansion properties.
e alloy) has been developed and improved.

More specifically, the invar alloy contains 34 to 37% of nickel in iron, and is in the vicinity of room temperature (0 to 2%).
(00 ° C.) is as low as about 1.5 × 10 ⁻⁶ / ° C. The mechanism of the low expansion property of the Invar alloy is based on a spontaneous volume magnetostriction effect generally called an “Invar effect”.

The super-invar alloy is prepared by alloying 4 to 6% of cobalt in an iron-nickel substrate, and has a coefficient of thermal expansion of about 0.5 × 1 near room temperature.
0 ⁻⁶ / ° C., which is lower than that of Invar alloy, and is excellent in low expansion property.

[0007]

However, although these low-expansion cast irons have excellent low-expansion properties, the low-expansion cast irons have a base structure of austenitic iron, and thus have low physical properties and mechanical properties. This was the cause, and a high Young's modulus could not be obtained.

[0008] The Young's modulus is a ratio of a simple tensile stress applied to an object to a strain generated in parallel with the tension. In the case of austenitic iron containing Ni, the Young's modulus shows a characteristic low value. Specifically, 110-1
The value was 30 GPa.

As described above, since the conventional low-expansion cast iron has a low Young's modulus, it is necessary to increase the thickness of the component in order to obtain high dimensional accuracy. This has been a major impediment to reducing machine weight and cost.

[0010] Further, since parts using low expansion cast iron are required to have high dimensional accuracy, in addition to thermal deformation, it is required to reduce elastic deformation due to stress. But,
As described above, low expansion cast iron has a low Young's modulus and a large part thickness, so that component segregation in cast parts occurs, and this component segregation adversely affects the coefficient of thermal expansion itself, resulting in low expansion. However, there was a problem that the property could not be maintained.

Further, in the conventional low expansion cast iron, in order to improve the low expansion property, there is a limitation in that the alloy matrix has an alloy composition that is largely different from the composition of the invar alloy or super invar alloy. For this reason, it was possible to obtain only low-expansion cast iron having an excellent low-expansion property but a relatively low Young's modulus.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has developed a low-expansion cast iron having improved Young's modulus while maintaining low-expansion properties, and a method for producing the same. An object of the present invention is to provide a low-expansion cast iron capable of realizing weight reduction and cost reduction of a part using the expanded cast iron, and a method for manufacturing the same.

[0013]

The high Young's modulus low expansion cast iron according to claim 1 is, by weight%, C: 0.6-2.0%, N
i: 25 to 40%, Co: 0.1 to 12.0%, Ni +
Co: 34 to 40%, Si: 1.0% or less, Mn: 1.
0% or less and Ti, Zr, Hf, V, Nb, Ta, C
One or several kinds of metal elements selected from r, Mo and W are used alone or in combination to contain 0.5 to 6.0%, the balance being Fe and unavoidable impurities, and having a solid solution carbon content of 0%. .4% or less.

The high Young's modulus low expansion cast iron according to claim 2 is
By weight%, C: 0.8 to 1.5%, Ni: 28 to 37
%, Co: 1.0 to 7.0%, Ni + Co: 34 to 37
%, Si: 0.3% or less, Mn: 0.3% or less and T
i, Zr, Hf, V, Nb, Ta, Cr, Mo or W
One or several metal elements selected from the group consisting of 1.0 to 4.0%, alone or in combination, with the balance being Fe and unavoidable impurities and having a solid solution carbon content of 0.4%;
% Or less.

In the first and second aspects of the present invention, first, a large amount of Ni (nickel) is contained as much as 25 to 40%, and the amount of dissolved carbon (a part of the total carbon amount C) and the amount of Si are increased.
Low expansion is realized by reducing the content of (silicon).

Ni is a component that produces the Invar effect (low expansion due to the spontaneous magnetostriction effect) and contributes to the reduction of the coefficient of thermal expansion. In the present invention, the content of Ni is 25 to 40.
% Is specified because the coefficient of thermal expansion increases if the Ni content is out of the specified range. When the Ni content is 28 to 37%, a low expansion cast iron having more excellent properties can be obtained.

Co (cobalt) is an element that further reduces the coefficient of thermal expansion of cast iron due to a synergistic effect with Ni when the total amount of Co and Ni is in the range of 34 to 40%. When the Co content exceeds 12%, the coefficient of thermal expansion increases conversely. Co is added in accordance with the required coefficient of thermal expansion, and the effect becomes significant by adding 1% or more.

C (carbon) is a component that imparts castability and machinability to cast iron. The higher the amount of C contained in the matrix in solid solution, the higher the Young's modulus of the low expansion cast iron. Element. In the present invention, the addition amount of C is 0.6 to
Although specified as 2.0%, if the content of C is less than 0.6%, it becomes impossible to secure the precipitation (or crystallization amount) of graphite which plays a role of improving the machinability, and the Young's modulus increases. This is because The content of C is 2.0%
This is because, if it exceeds, the coefficient of thermal expansion increases.

Si (silicon), like C, is a component that imparts castability and machinability to cast iron. In the present invention, the addition amount of Si is specified to be 1.0% or less. However, when the content of Si exceeds 1.0%, the coefficient of thermal expansion increases.

Mn (manganese) is a basic component of cast iron and is an element that functions as a deoxidizer and a component for improving corrosion resistance in addition to improving mechanical strength. Further, Mn is an element having a particularly large effect of increasing the coefficient of thermal expansion. When the amount of solid solution of Mn increases, the Young's modulus slightly increases, but the content of Mn must not exceed 1.0%. There is.

In the high Young's modulus low expansion cast iron of the present invention, the Young's modulus is increased by alloying elements other than Ni, Co, C, Si and Mn described above. The Young's modulus of an alloy is related to the bonding force of a crystal lattice composed of a base element, and the Young's modulus increases as the amount of an element that forms a stable solid solution increases.

In the low expansion cast iron of the component system based on Fe and Ni according to the present invention, the periodic table according to the IUPAC (International Union of Pure and Applied Chemistry) inorganic chemical nomenclature is used as an element for efficiently improving the Young's modulus by solid solution. Are found to be suitable. That is, specifically, Ti (titanium), Zr (zirconium), V (vanadium), Nb (niobium), Ta (tantalum), Cr
(Chromium), Mo (molybdenum) and W (tungsten), which replace the atoms of the iron and nickel based crystal lattice and enter the crystal lattice to increase the interstitial bonding force. It is. These elements are effective when added alone or in combination of two or more elements in the case of composite addition. In particular, in the case of composite addition, the effect of improving the Young's modulus of each element acts additively. However, when many of these elements form a solid solution, they increase the thermal expansion coefficient of low expansion cast iron. For this reason, in order to make the thermal expansion coefficient in the range from room temperature to 100 ° C. not more than 5.0 × 10 ⁻⁶ / K, it is necessary to make the total amount of addition less than 6.0%. When the total amount of the additives is less than 0.5%,
Since the above effects cannot be obtained, the addition amount is defined as 0.5 to 6.0%. In addition, the total amount of the addition amount is 1.0 to 4.0%.
Then, the Young's modulus can be further improved.

The third aspect of the present invention provides the first and second aspects.
In the described high Young's modulus low expansion cast iron, Mg or Ca
Is characterized in that at least one of the residual amounts is 0.02 to 0.10% and the graphite is spherical graphite.

According to the present invention, spheroidal graphite having a spheroidization ratio of 80% or more can be obtained by setting the residual amount of Mg or Ca to 0.02 to 0.10%. M
The reason why the residual amount of g or Ca is defined as 0.02 to 0.10% is that when the residual amount is less than 0.02%, the spheroidization ratio of graphite is reduced, and the residual amount is 0.1 to 0.1%. If it exceeds 10%, the thermal expansion coefficient is increased, and an intermetallic compound is formed to impair the machinability. Spheroidal graphite having a spheroidization ratio of 80% or more is used because when the spheroidization ratio of graphite is low and when flake graphite is used, the Young's modulus is sharply reduced.

According to a fourth aspect of the present invention, there is provided the high Young's modulus low expansion cast iron according to any one of the first to third aspects,
An area ratio of carbide precipitates excluding graphite is 3% or less.

Ti, Zr, which are elements of Groups 4 to 6 of the periodic table,
When V, Nb, Ta, Cr, Mo and W are added in excess of 1.0%, a part thereof precipitates as carbide in the cast structure. When carbides precipitate in large amounts at the grain boundaries, the Young's modulus decreases, but when carbides are dispersed and precipitated in the grains, they have excellent properties for improving tensile strength and proof stress. However, even when carbides are dispersed and precipitated in the grains, the Young's modulus is not improved.

As described above, the elements of Groups 4 to 6 of the periodic table to be added are dissolved as solid solutions and consumed as carbides.
It is desirable that these elements contribute to the improvement of Young's modulus as much as possible. For this reason, by performing an appropriate heat treatment described later, it is possible to decompose the grain boundaries and carbides in the grains. Actually, in the low expansion cast iron of the present invention, 9
By maintaining the temperature at a temperature of 00 to 1200 ° C., the Young's modulus can be effectively increased by setting a treatment time in which the carbide remaining in the metal structure has an area ratio of 3% or less.

According to a fifth aspect of the present invention, there is provided a method for producing a high Young's modulus low expansion cast iron comprising C, Ni, Co, Si, Mn and Fe, and Ti, Zr, Hf, V, Nb, Ta, Cr, Mo.
Or a cast iron material containing one or several kinds of metal elements selected from W is melted, and the molten material is poured into a mold to obtain cast iron.
It is characterized by performing a heat treatment for heating to a temperature range of 1200 ° C.

According to the present invention, by performing the heat treatment at a temperature of 900 to 1200 ° C., the area ratio of carbide precipitates remaining in the metal structure can be reduced to 3% or less, and the Young's modulus can be improved. Thus, a high Young's modulus low expansion cast iron can be obtained.

According to a sixth aspect of the present invention, in the method for producing a high Young's modulus low expansion cast iron according to the fifth aspect, after the heat treatment,
After cooling to a temperature range of 00 to 850 ° C. and maintaining the cast iron at the above temperature, a cooling process of cooling to room temperature at a cooling rate higher than air cooling is performed.

Carbon tends to form an interstitial solid solution in the crystal lattice of the base of the low-expansion cast iron, and the lattice distortion is increased so that the bonding force is reduced and the Young's modulus is lowered. Fortunately, reducing the amount of solid solution of carbon is also effective in reducing the coefficient of thermal expansion. Therefore, in order to reduce the amount of solid solution of carbon,
It is effective to maintain a temperature of 600 to 850 ° C. to precipitate stable graphite. According to the present invention, the amount of dissolved carbon is controlled to 0.1 to 0.4%, and the other carbon is substantially graphite and partially exists as carbide. Therefore, according to the present invention, the coefficient of thermal expansion can be reduced and the Young's modulus can be improved.

In order to realize both a heat treatment for decomposing carbides at a higher temperature and a heat treatment for graphitizing at a lower temperature, it is necessary to continuously reduce the temperature from the carbide decomposition temperature to the graphitization heat treatment temperature in a furnace. It is valid. Therefore, according to the present invention, before the carbon dissolved in the matrix at a high concentration forms a carbide again, in the treatment of decomposing the carbide, the stable phase graphite is used to make Young by the solid solution element. The effect of improving the rate can be maximized.

According to a seventh aspect of the present invention, in the method for producing a high Young's modulus low expansion cast iron according to the sixth aspect, after the cooling treatment,
Annealing is performed in a temperature range of 100 to 400 ° C.

If there is residual strain in the low expansion cast iron,
It causes dimensional changes over time and lowers Young's modulus. For this reason, the residual distortion can be removed by performing annealing for removing the final distortion after processing as in the present invention.

In the present invention, the heating conditions in the temperature range of 100 to 400 ° C. are specified.
For example, when annealing at a temperature of 400 to 650 ° C., the thermal expansion coefficient increases because Ni of the base of the low expansion cast iron causes segregation.

According to an eighth aspect of the present invention, in the method for producing a high Young's modulus low expansion cast iron according to the fifth aspect, at least one element of Mg or Ca is added immediately before pouring the molten material into the mold. It is characterized by.

According to the present invention, immediately before pouring the molten material into the mold, the Mg or Ca element is injected to reduce the residual amount of Mg or Ca to 0.02 to 0.10%. It is possible to obtain spherical graphite having a spheroidization ratio of 80% or more. In order to make the residual amount of Mg or Ca 0.02 to 0.10%, the amount of added Mg or Ca should be 0.02 to 0.10%, which is the residual amount.
% Is preferably 20 to 30 times.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to examples and comparative examples.

Example 1 (Tables 1 and 2; Sample Nos. 1 to N)
o. 12) In this example, a case will be described in which Cr and W are added as elements of Groups 4 to 6 of the periodic table according to IUPAC inorganic chemical nomenclature.

In this example, the cast iron materials shown in Table 1 were used.

[0041]

[Table 1]

As shown in Table 1, Sample No. 1 to N
o. Up to 12 cast iron materials have Cr and W added.

Sample No. No. 1 to No. Each of the cast iron materials up to 12 was melted using a high-frequency electric furnace having a capacity of 25 kg, and then poured into a 1-inch Y-block mold of a furan sand type to produce cast iron, and each as-cast material (as cast) was prepared. Obtained. Each of these as-cast materials was subjected to a heat treatment in the air in a heat treatment furnace at 1200 ° C. for 4 hours, then cooled to 750 ° C. by furnace cooling, held for 4 hours, and air-cooled to obtain a heat treated material. further,
This heat-treated material was annealed at 350 ° C. for 24 hours to obtain an annealed material.

The thus obtained sample No. No. 1 to No. The thermal expansion coefficient and Young's modulus of each of the as-cast materials, heat-treated materials and annealed materials up to 12 were measured. Table 2 shows the measurement results.

In the measurement of the coefficient of thermal expansion, a test piece having a diameter of 5 mm and a length of 65 mm was prepared according to JIS G551.
1 A thermal expansion test was conducted in accordance with the thermal expansion test method specified in “Iron-based low expansion cast iron products”, and the temperature range from room temperature to 100 ° C for each as-cast, heat-treated and annealed cast alloy Was measured for the average coefficient of thermal expansion.

In the measurement of the Young's modulus, an ultrasonic pulse is transmitted to a test piece to measure a sound velocity and an ultrasonic direct contact method (also called an ultrasonic pulse method) for detecting an acoustic discontinuity. Measured.

[0047]

[Table 2]

The Young's modulus of conventionally used austenitic iron such as invar alloy and super invar alloy was 110 to 130 GPa. No. 1 to No. The Young's modulus of each of the as cast materials up to 12 shows a value of 140 GPa or more, and the Young's modulus can be improved by adding Cr and W. Further, the addition of Cr and W greatly increases the coefficient of thermal expansion.

Further, by heat treating the as-cast material, Cr carbide and W carbide can be decomposed and the amount of solute carbon can be reduced by graphitization, so that the Young's modulus shows a value of 150 GPa or more.
Young's modulus increased while the coefficient of thermal expansion decreased.

Further, it was observed that the annealing at 350 ° C. released the residual stress, which slightly increased the Young's modulus.

In this example, since the test Y-block was used, no significant residual stress appeared to occur in heat treatment and machining, but the effect of annealing was confirmed. The amount of carbide after the carbide decomposition heat treatment was approximately 3% or less.

Example 2 (Tables 3 and 4; Sample Nos. 13 to
No. 22) In this example, C was added as a Young's modulus improving additive element.
Dissolution experiments were also performed on elements other than r and W, and their effects were confirmed.

Each cast iron material having the composition shown in Table 3 was used.

[0054]

[Table 3]

A test was conducted in the same manner as in Example 1 using each of the cast iron materials having the component compositions shown in Table 3. The result is
It is shown in Table 4.

[0056]

[Table 4]

As shown in Table 4, Ti, Zr, Hf,
The effect of improving the Young's modulus was confirmed when any of V, Nb, Ta and Mo was added. Further, as in the case of the composite addition of Cr and W in Example 1, an additive effect was also confirmed when the element was compositely added.

Comparative Examples (Tables 5 to 6; Sample Nos. 23 to N)
o. 29) In this comparative example, Ti, Zr, Hf, V, Nb, T
The case where a cast iron material to which the metal elements a, Cr, Mo and W are not added within the scope of the present invention will be described.

In this comparative example, the cast iron materials shown in Table 5 were used.

[0060]

[Table 5]

As shown in Table 5, Sample No. 23 and No. 23. In Sample No. 24, the metal elements of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W, which are the additives for improving the Young's modulus of the present invention, were not added.
26 and No. 26. In No. 27, the above-mentioned metal elements are added more than prescribed.

A test was conducted in the same manner as in Example 1 using each cast iron material having such a component composition. Table 6 shows the results.

[0063]

[Table 6]

As shown in Table 6, Sample No. 23 to N
o. In a cast iron material having a component composition of up to 29, the Young's modulus shows a low value of 130 GPa or less.

The sample No. to which W was added in a large amount up to 7.0% was used. 26 shows a high Young's modulus, but has a low expansion coefficient of 6.0 × 10 ⁻⁶ / K or more,
A high Young's modulus could not be obtained while maintaining low expansion properties.

Sample No. 27, the total amount of Ti and Cr added was 8%, and the Young's modulus after heat treatment was 164 G
Although it is as high as Pa, the coefficient of thermal expansion has risen to 7.0 × 10 ⁻⁶ / K or more. Thus, Ti, Zr, Hf, V,
The addition of metal elements of Nb, Ta, Cr, Mo and W is as follows:
The addition of 0.5% or more effectively increases the Young's modulus. However, when the total amount exceeds approximately 6%, the thermal expansion coefficient increases and the result exceeds 5.0 × 10 ⁻⁶ / K. It is had.

The sample No. In No. 28, since the residual amount of Mg was 0.01%, graphite became flaky. Therefore, the Young's modulus is a low value of about 110 GPa. Sample No. 25 and sample no. 29 means S
Since i and the total amount of Ni and Co exceeded the proper range of the present invention, the result was that the coefficient of thermal expansion exceeded 5.0 × 10 ⁻⁶ / K.

Therefore, according to the present embodiment, as is apparent from the comparison results from Example 1, Example 2, and Comparative Example, by setting the composition of the cast iron material to an appropriate range and performing heat treatment or the like, A high Young's modulus low expansion cast iron having a high Young's modulus can be obtained while maintaining low expansion properties.

[0069]

As described above, according to the method for producing a high Young's modulus low expansion cast iron of the present invention, the low expansion coefficient is 5.0.
Since it is possible to obtain a low-expansion cast iron having a high Young's modulus improved to 150 GPa or more while keeping it low at ^10-6 / K or less, low thermal expansion properties are required, and the thickness is reduced and the weight is reduced. It is possible to provide a cast iron suitable for a machine part or the like that requires the conversion.

Claims (8)

[Claims] C. 0.6 to 2.0% by weight, N
i: 25 to 40%, Co: 0.1 to 12.0%, Ni +
Co: 34 to 40%, Si: 1.0% or less, Mn: 1.
0% or less and Ti, Zr, Hf, V, Nb, Ta, C
One or several kinds of metal elements selected from r, Mo and W are used alone or in combination to contain 0.5 to 6.0%, the balance being Fe and unavoidable impurities, and having a solid solution carbon content of 0%. 0.4% or less, high Young's modulus low expansion cast iron. 2. C: 0.8-1.5% by weight, N
i: 28 to 37%, Co: 1.0 to 7.0%, Ni + C
o: 34 to 37%, Si: 0.3% or less, Mn: 0.3
% Or less and Ti, Zr, Hf, V, Nb, Ta, C
One or several kinds of metal elements selected from r, Mo and W are used alone or in combination to contain 1.0 to 4.0%, the balance being Fe and unavoidable impurities, and having a solid solution carbon content of 0%. 0.4% or less, high Young's modulus low expansion cast iron. 3. The cast iron according to claim 1, wherein the residual amount of at least one of Mg and Ca is 0.02 to 0.10% and the graphite is spheroidal graphite. High Young's modulus low expansion cast iron. 4. The high Young's modulus low expansion cast iron according to claim 1, wherein an area ratio of carbide precipitates other than graphite is 3% or less. Expansion cast iron. 5. C, Ni, Co, Si, Mn and Fe
Containing Ti, Zr, Hf, V, Nb, Ta, Cr,
After melting a cast iron material containing one or several kinds of metal elements selected from Mo and W, pouring the molten material into a mold to obtain a cast iron,
A method for producing a high Young's modulus low expansion cast iron, comprising performing a heat treatment of heating to a temperature range of 0 to 1200 ° C. 6. The method for producing a low Young's modulus cast iron according to claim 5, wherein after heat treatment, the cast iron is cooled to a temperature range of 600 to 850 ° C., and the cast iron is held at the temperature, and then cooled at a cooling rate equal to or higher than air cooling. A method for producing a high Young's modulus low expansion cast iron, which comprises performing a cooling treatment for cooling to room temperature. 7. The method for producing a high Young's modulus low expansion cast iron according to claim 6, wherein annealing is performed in a temperature range of 100 to 400 ° C. after the cooling treatment. 8. The method for producing a high Young's modulus low expansion cast iron according to claim 5, wherein immediately before pouring the molten material into the mold,
A method for producing a high Young's modulus low expansion cast iron, wherein at least one element of Mg or Ca is added.